1. Field
The present disclosure relates to an integrated member integrally formed by welding together a first member and a second member wherein the first and second members have different mechanical characteristics, and a method for manufacturing the integrated member.
2. Description of the Related Art
A starter-driven gear for transmitting a driving force of a starter motor of a vehicle to a crankshaft of an engine can be manufactured by integrating a shaft component made of alloy steel and a gear component made of carbon or alloy steel. The gear component can have an annular configuration and be formed with teeth on its outer circumference via electron beam welding. In some cases, since the shaft component is to be mounted on a vehicle via bearings fitted on the outer and inner circumferences of the shaft component, it is desired that the shaft component has high hardness. On the other hand, it may be sufficient that the gear component has sufficient strength to withstand meshing with a mating gear, and thus the shaft component would not be required to have as much hardness, but instead be required to suppress its hardness to a moderate degree in order to prevent breakage of gear teeth.
One manufacturing method has been proposed, for example, in Japanese Application No. 285428/2004, as a technology for welding two members together, each member having different mechanical characteristics. That is, a shaft component, prior to welding, can be formed with a carburized layer (e.g. a preparatory carburized layer) by performing carburizing-quenching and tempering. The shaft component and the preparatory carburized layer of the shaft component to be welded to a gear component can be removed by cutting, or other removal procedures. Then, the gear component can be press-fit to the portion of the shaft component from which the preparatory carburized layer is removed, where the shaft component and the gear component can be integrally welded to each other to form an integrated member. The obtained integrated member can be further treated by carburizing-quenching and tempering, or carbonitriding-quenching and tempering, to form a starter-driven gear having desired mechanical characteristics (i.e. the shaft component having deeper carburized layer and higher hardness than those of the gear component).